Close to Pearson, your best bet would be the bakery inside Dixie Park mall at Eastgate and Dixie Road (North-East corner). Grab a bubble tea with soft-serve ice cream while you're there too. You haven't lived until you've had bubble tea with ice cream in it.

If you are willing to travel a bit more, Akko Cake House at Burnhamthorpe and Creditview (NW corner of the intersection, NW corner of the plaza) makes some really good... everything.